Solid state motor starting apparatus

ABSTRACT

A motor starting switch providing a predetermined time delay before permitting reenergization of a motor upon deenergization thereof comprises a generally cup-shaped casing having an open end adapted to receive a single or dual solid state starting elements. The dual elements are adapted to be coupled in series or parallel electrical circuit relation. An electrically conductive clip is disposed at the open end of the casing and provides electrical contact, serves as a casing half and maintains a mechanical bias on the solid state starting elements. The switch is provided with plug on terminals so that the switch can be directly plugged into a motor for starting thereof.

United States Patent 1191 1 Larsen et a1.

1111 3,794,949 1451 Feb. 26, 1974 SOLID STATE MOTOR STARTING APPARATUS[75] Inventors: Odd Larsen, Kenyon, R.l.; Carl N.

Johnson, Bridgewater, Mass.

[73] Assignee: Texas Instruments incorporated,

Dallas, Tex.

[22 Filed: Feb. 1, 1973 21 Appl. No.2 328,553

[52] US. Cl. 338/22 R, 310/68 C [51'] Int; Cl H0lc 7/04 [58] Field ofSearch 338/22, 23, 25; 310/68 C; 318/471-473 [56] I References Cited vUNITED STATES PATENTS 3,695,054 10/1972 Barry 318/473 X 2,376,863 I5/1945 Bussmann... 318/473 x 2,417,912 3/1947 Clark 318/473 X 2,523,0599/1950 Richer! et a1. 310/68 C Primary ExaminerC. L. Albritton Attorney,Agent, or Firm-John A. l-iaug; Edward J. Connors, Jr.; James P.McAndrews [57] ABSTRACT A motor starting switch providing apredetermined time delay before permitting reenergization of a motorupon deenergization thereof comprises a generally cup-shaped casinghaving an open end adapted to re-' ceive a single or dual solid statestarting elements. The dual elements are adapted to be coupled in seriesor parallel electrical circuit relation. An electrically conductive clipis disposed at the open end of the casing and provides electricalcontact, serves as a casing half and maintains a mechanical bias on thesolid state starting elements. The switch is provided with plug onterminals so that the switch can be directly plugged into a motor forstarting thereof. 1

15 Claims, 18 Drawing Figures PATENIED FEB 2 61974 SHEET 6 BF 9 PATENIEDFEB26 2B1"? SHEET 8 0F 9 SOLID STATE MOTOR STARTING APPARATUS Thisinvention relates generally to motor control systems and moreparticularly to a solid state device for controlling the power suppliedtothe windings of an electric motor. In various types of electric motorssuch as single phaseac. motors a pair of windings are typically employedconnected ir'rparallel relationship with each other and are commonlyidentified asthe start winding and the run winding. Such motorstypicallyrequire certain types of starting systems including switching devicesfor energizing and deenergizing the start winding. Typically duringstarting of such motors the start winding is energized as well as themain winding during the motor starting period, while the start windingis substantially deenergized as the motor approaches its running speed.

Electromechanical relays are available for starting such motors as shownfor instance in US. Pat. Nos.

' is the provision of a housing in which single or dual plugged onto amotor for starting thereof. Another obthe present invention. In relaysof this type some parameter is sensed, such as main winding current, and

the state of energization of the start winding is effected uponrealization of a predetermined level .of the parameter. As shown in theabove-referenced patents a solenoid is energized by main winding currentwhenit reaches a predetermined, level causing a movable contact to movethereby deenergizing the start winding.

The provision of such devices has however, presented certain problems inview of the inherent .unreliability of mechanical switching devices whenexposed to the adverse environment associated with continual opening andclosingof the contacts and the accompanying sparking and arcing. As aresultrapid wear and degradation of the contacts may occur necessitatingfrequent replacement as well as presenting a potential danger of motorfailure. In copending, coassigned application Ser. No. 132,846 filedApr. 9, 1971, a plurality of resistance elements each possessing aresistance characteristic having a positive temperature coefficient anda sharply defined transition temperature above which the resistance ofthe element increases relatively abruptly, hereinafter. referred to asPTC elements, are employed to provide a switching device permittingenergization of the start winding of the motor for a predetermined timeinterval sufficient for the motor to approach running speed at whichtime the transition temperature of the PTC elements is approachedcausing the resistance thereof to increase rapidly thereby blockingcontinued current flow therethrough essentially deenergizing the startwinding. Theseelements have proven to be very effectivefare lessexpensive, more reliable andlonger livedthan the electromechanicalrelays they replaced. For many applications, particularly when the PTCstarting device is coupled across ject is the provision of a startingdevice which, after being previously energized, provides a predeterminedtime delay upon deenergization before the motor can be reenergized.Various additional objects and advantages will become readily apparentfrom the following detailed description.

The invention accordingly comprises the elements and combination ofelements, features of construction and manipulation and arrangements ofparts, all of which will be exemplified in the structure hereinafterdescribed, and the scope of the application of which will be indicatedin the appended claims.

Briefly, the realization of these objects are obtained by providing acup-shaped electrically insulative casing having an open end whichreceives PTC elements therein. An electrically conductive clip isdisposed over the open end of the casing and is provided with twoslotted end portions which fit over ears in the casing wall to anchorthe clip in location with a bias applied to the PTC elements. The casingcan accommodate various bayonet type contact-terminals which facilitateelectrical connection of a single element or of dual elements in seriesor in parallel circuit relationship. The casing also includes femaleplug-on pin connectors connectable to the bayonet type terminals so tatthe device can be. plugged directly to pins provided on the motor. Thematerial chosen for the electrically conductive contact coating on thePTC elements and that of the terminals and clip is such as to militateagainst breakdown or corrosion of the conductive coatings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front plan view of aswitch made in accordance with the invention mounted on a compressormotor shown broken away;

FIG. 2 is a right plan view of the FIG. 1 switch;

FIG. 3. is a right plan view similar to FIG. 2 of a seca run capacitorwhere voltage developed across the PTC device may approach values inexcess of twice the line voltage it may be desirable to use a pluralityof FIG. 4 is a front plan view of the switch casing; FIG. 5 is a leftplan view of the FIG. 4 casing;

FIG. 6 is a right plan view of the FIG. 4 casing; FIG. 7 is a bottomplan view of the FIG 4 casing; FIG. 8 is a top plan view of the FIG. 4casing;

FIG. 9 is a perspective view of a spring contact receivable on the FIG.4 casing;

FIG. 10 is a perspective view of another spring contact employed in theFIG. 2 switch;

FIG. 11 is perspective view of a combination terminal-contact employedin the FIG. 2 switch;

FIG. 12 is a perspective view of a combination terminal-contact employedin the FIG. 3 switch;

FIG. 13 is a perspective view of a PTC element employed in the FIG. 2and FIG. 3 switches; 7

FIG. 14 is a perspective view of a PTC element employed in a switchsimilar to FIG. 3;

FIG. 15 is a cross sectional view taken on lines 15-l5 of FIG. 2;

FIG. 16 is a cross sectional view taken on lines 16-16 of FIG. 3;

FIG. 17 is a cross sectional view similar to FIG. 16

but showing a single PTC element; and

FIG. 18 is a schematic electrical circuit showing how the FIGS. 1-17switches can be employed for starting an electric motor having a run anda start winding.

In the following detailed description corresponding elements in thevarious views of the drawings are indicated by common referencenumerals.

As seen in FIG. I, switch is mounted on a compressor 12, only partlyshown. With particular reference to FIGS. 4-8, switch 10 comprises acasing member 14 which has a cup-shaped portion having a bottom wall 16and a depending generally cylindrical side wall 18. The cup-shapedportion has an open end 20 for reception of one or more PTC switchingelements to be discussed infra. A pair of notches 22, 24 are formed inthe free distal end of wall 18 and cars 26, 28 protruding from the outerperiphery of wall 18 are aligned so that each is directly below arespective notch. Each ear has a surface which tapers toward the slot tofacilitate placement of a clip thereover, and preferably is providedwith a groove on the opposite end'of the ear to lockingly receive theclip as will be explained in greater detail below. A terminal receivingslot 30 is formed in the side wall near bottom wall 16 and may extendslightly into the bottom wall. Another slot 32 is formed in the bottomwall 16 in close proximity to the side wall and in alignment with notch24 and ear 28.

Casing member 14 is formed with a second pin receiving portion havingpin receiving apertures 34, 36, 38 receiving therein respective femalepin connectors B, C, A. A leg 40 depends from casing 14 and is used topush the device onto terminal pins of a motor. On the side of the casingremote from leg 40 a plurality of stop tangs 42 project from the casingadjacent the pin receiving apertures to limit motion of thecasing whenit is pushed onto the motor pins so that the pin connectors A, B, C willnot contact the glass header portion surrounding the motor pins, as seenin FIG. 1.

Clip member 44, depicted in FIG. 9, is generally U- shaped having twoleg portions 46, 4 8 depending from a bight portion 50 and isconstructed of electrically conductive material having good springcharacteristics. Bight portion 50 is formed with a plurality oflaterallyextending smooth .wave like depressionsto increase the area of contactwith PTC'elements disposed in the casing and to enhance the spring biasof the clip against the PTC elements. In general it is preferred thatthesurface of electrical connection with the PTC elements be as large aspossible in order to lower current densities and prolong contact life. Aslot52 is formed in'leg 46 and a similar slot 54 is formed in leg 48.Distal free end of legs 46, 48 are formed with laterally extending tabs56,58 respectively. Clip 44 is disposed over the open end 20 of casing14 with slots 52, 54 received over cars 26, 28. It should be noted thatpreferably clip 44 does not entirely close the open end 20 to permitcirculation of air therethrough.

In FIG. 10 an electrical contact member 60 composed of electricallyconductive material having good spring characteristics, is shown havinga plate like member also formed with a plurality of laterally extendingwa've'like depressions to improve electrical connection with the PTCelements and is provided with a downwardly extending arm 62. Contactmember 60 is received on bottom wall 16 with arm 62 extending throughslot 32, however as described below is used only in certain embodimentsof the invention.

leg 74 is received between wall 16' and two: abutting Two differentcontact-terminals 64, 66 are shown in FIGS. 11 and 12 respectively.Terminals 64, 66' are both generally L-shaped with respective legs 68,70 formed into bayonet type terminals. Respective legs 72, 74 serve ascontact elements and are adapted to extend into casing 14 with theterminal portion projecting out through slot 30. Laterally extendingtabs 76 formed in contact terminal 64 are further removed from leg 72than corresponding laterally extending tabs 78 in contact-terminal 66.Tabs 76 and 78 are received on the bottom wall surface 16 and limitinward movement of the respective contact. terminal. Thus, contact leg72 will'be spaced further from the inside surface of bottom wall 16 thanleg 74. Choice of which contact terminal member to be used depends onthedesired mode of operation, as explained below.

FIGS. 13 and 14 show two different generally disk shaped PTC elements 80and 82 respectively. Itwill be noted that element 82 is considerablythicker than 80, preferably twice as thick. The FTC elements possess aresistance characteristic having a positive temperature coefficient anda sharply defined transition temperature above which the resistance ofthe elements increases relatively abruptly. Typical examles of such' PTCelements maybe fabricated of barium titanate doped with a rare earthsuch. as lanthanum. Each elemember 60 is received between one PTCelement 80 and wall 16 with arm 62 extending through slot 30 and fixedlyattached to tab 58 of clip 44, as by welding. The

other tab 56 of clip 44 is similarly attached to an extension of pinconnector B which connector is disposed in pin aperture 36. Terminal leg68 of contact-terminal 64 is connected to connector C as by welding sothat the PTC elements are connected in parallel circuit relationship.Thus the circuit path may be traced from pin connector 8 to tab 56, clip44 with one branch'going throughone PTC element 80 to contact plate 72,and a second branch going to arm 62 to plate 60 and through the secondPTC element 80 to contact plate 72 and then to terminal leg 68 and pinconnector C. This mode of operationis particularly advantageous since itminimizes current density through the PTC contact coatings and henceimproves contact life.

FIG. 16 depicts an alternate embodiment in which the two PTC elements 80are arranged in series circuit relationshipsin switch 10. In thisarrangement contact FTC elements 80. In this embodiment the circuit pathruns from pin connector B to tab 56, clip 44 through both PTC elements80 to contact plate 74, to terminal leg 70 and pin connector C.

If desired a single PTC element can be employed as shown in FIG. 17. Inthis embodiment the same contact-terminal member is used as in the FIG.16 embodiment. The electrical path is also the same as in the seriesconnected elements, the two stacked PTC elements of FIG. 16corresponding to the single thicker PTC element of FIG. 17. Theremaining structure of FIGS. 16 and 17 are identical to that of FIG. andhence need not be redescribed.

Terminal pin connector A need not be employed for applications in whicha direct connection is made to the motor. FIG. 18 depicts how the switchof the instant invention may be employed. Pin connector A is conment(s)in its low resistance mode current passes through the PTC elements andthe start winding W as well as through the run winding W By the time themotor has reached its running speed the PTC element(s) has heated up andgone into its high resistance mode effectively deenergizing the startwinding. The PTC element(s) is maintained in its high resistance mode aslong as power is applied to the motor due to the voltage across terminalA C.

The materials chosen for electrically conductive coatings 84 on PTCelements 80, 82 and the elements inphysical contact therewith e.g.members 44, 60, 72 and 74 are chosen so current is evenly distributedand with little or no resistive heating and so that any tendency tocorrode is minimized. That is they are chosen so that the material forthe coatings and the contacting members are either the same or aregalvanically compatible to minimize any tendency of corrosion whichwould decrease the useful life of the device. Thus, for

' example, either silver, nickel or aluminum could be used for both thecoatings and the contacting members. Alternatively, aluminum could beemployed for the coatings and indium or cadmium for the contactingmembers. Y

By combining into the single clip member 44 the functions of electricalcontacting, serving as a casing half and maintaining mechanical bias onthe PTC elements improved yield is obtained since fewer parts arerequired and hence dimensional tolerances required to obtain thenecessary force of the clip against the PTC element(s) is more easilyachieved. Clip 44 does not completely enclose the open end of the casingso that cooling of the PTC elements is promoted and also provision ismade foroutgassing of organic vapors which otherwise wouldcausedeterioration of the PTC characteristic. I

Whe a motor has been started with a solid state switch made inaccordance with the invention the PTC element(s) is maintained in thehigh resistance mode so that upon deenergization of the motor for anyreason reenergization cannot be accomplished until the PTC element(s)cools and returns to its low resistance mode. Clip 44 allows circulationof air so that the PTC pills will cool at a desired rate, for exampletwo minutes. Thus the switch'is particularly useful when it is de-.

Thus it will be seen from the above description that the severalenumerated objects of the invention have been realized. I

Although the invention has been described with respect to specificpreferred embodiments thereof, many variations and modifications willimmediately become apparent to those skilled in the art. It is thereforethe intention that the appended claims be interpreted as broadly aspossible in view of the prior art to include all such variations andmodifications.

We claim:

1. A solid state switch comprising a generally cupshaped casing formedof electrically insulative material, the casing having a bottom wall anda side wall depending therefrom forming a switch cavity, the side wallhaving a distal free end forming an open end of the casing, two notchesare formed in the distal free end portion of the side wall, two cars areformed on the outer peripheral surface of the side wall, one inalignment with each notch, an aperture is defined in a casing wall;electrically conductive means is disposed on the bottom wall in theswitch cavity and extends from within the cavity through the aperture toa point outside the casing; electrical resistor means is disposed in theswitch cavity in electrical connection with the electricallyconductive'means disposed on the bottom wall; an electricallyconductive, generally U-shaped clip having first and second legsdepending from a bight portion, the legs each provided with a slot, theclip is disposed over the open end of the casing with the casing earsprojecting through respective leg slots, the bight extending through thenotches and having a smooth surface biased against the electricalresistor means spaced from the electrically conductive means.

2. A solid state switch accordingto claim 1 in which the bight of theelectrically conductive U-shaped clip is formed with a plurality oflaterally extending smooth wave like depressions to increase the'surfaceof contact engagement and enhance the bias of the clip against theelectrical resistor means. r

3. A solid state switch according to claim 1 in which the aperture inthe casing wall is located in the bottom wall, the means disposed on thebottom wall comprises anelectrically conductive plate formed of materialhaving good spring characteristics, the plate is formed with a pluralityof laterally extending smooth wave like depressions to increase thesurface of contact engagement and enhance the bias of theplate againstthe electrical resistor means, and an arm depends from the plate andextends through the aperture in the casing bottom wall and iselectrically connected to electrical terminal means.

4. A solid state switch according to claim 3 in which a second apertureis formed in a casing wall, the electrical resistor means comprises twodisk-shaped elements each having two spaced faces, a face of one elementin engagement with the electrically conductive plate, an electricallyconductive contactplate is interposed between the two elements,thecontact plate extends out of the casing through the second apertureand is connectable to an electrical source, and the electricallyconductive clip is in engagement with the other element. i

5. A solid state switch according to claim 1 in which the electricalresistor means comprises at least one generally disk-shaped elementcomposed of material having a positive temperature coefficient ofresistivity.

ing a plurality of stop surfaces projecting from the casing adjacent thefemale connectors to limit motion of 8. A solid state switch accordingto claim 1 in which the means disposed on the bottom wall comprises aflat plate which extends substantially across the switch cavity.

9. A solid state switch according to claim 1 in which the secondaperture is formed in a casing wall and an electrically conductive plateextends substantially across the switch cavity spaced from the bottomwall, the conductive plate also extending through the second apertureand electricallyconnected to electrical terminal means, the electricalresistor means comprising two electrical resistors, the conductive platebeing interposed between and in electrical connection with the twoelectrical resistors.

10. A solid state switch according to claim 1 in which the casing isformed with a portion mounting female connectors for terminal pins, onefemale connector electrically connected to the electrically conductiveclip, another female connector electrically connected to a portion ofthe means disposed on the bottom wall which is disposed outside theswitch cavity. 11. A solid state switch according to claim 10 in whichbayonet terminals project from the female connectors below the bottomwall of the casing, the casing is provided with a leg depending from thebottom wall extending beyond the bayonet terminals to facilitate pushingof the switch onto terminal pins.

12. A solid state switch according to claim 11 includthe switch ontoterminal pins.

13. A solid state switch according to claim 10 in which the legs of theU-shaped clip have laterally extending tabs at their face distal ends,the said one female connector having a portion extending therefromwelded to one of the tabs of the clip.

14. A solid state switch according to claim 1 in which the casing isformed with a portion mounting female connectors for terminal pins, thelegs of the U-shaped clip having laterally extending tabs at their freedistal ends, one female connector having a portion extending therefromwelded to one of the tabs of the clip, the other clip tab welded to aportion of the means disposed on the bottom wall which is disposedoutside the switch cavity, the electrical resistor means comprising twostacked resistor elements, electrical contact means interposed betweenthe two resistor elements and electrically connected to another femaleconnector.

15. A solid state switch comprising a casing having first and secondportions, a plurality of apertures in the first portion, female pinconnectors received in the respective apertures, a second portiondefining a switch cavity and having an open end, disk-like means havinga positive temperature coefficient of resistivity received in' thecavity, an electrically conductive clip received over the open end ofthe second portion and biased against the disc-like means, and meanselectrically connecting the clip and'a portion of the disc-like meansspaced from the clip to respective female pin connectors.

1. A solid state switch comprising a generally cup-shaped casing formedof electrically insulative material, the casing having a bottom wall anda side wall depending therefrom forming a switch cavity, the side wallhaving a distal free end forming an open end of the casing, two notchesare formed in the distal free end portion of the side wall, two ears areformed on the outer peripheral surface of the side wall, one inalignment with each notch, an aperture is defined in a casing wall;electrically conductive means is disposed on the bottom wall in theswitch cavity and extends from within the cavity through the aperture toa point outside the casing; electrical resistor means is disposed in theswitch cavity in electrical connection with the electrically conductivemeans disposed on the bottom wall; an electrically conductive, generallyU-shaped clip having first and second legs depending from a bightportion, the legs each provided with a slot, the clip is disposed overthe open end of the casing with the casing ears projecting throughrespective leg slots, the bight extending through the notches and havinga smooth surface biased against the electrical resistor means spacedfrom the electrically conductive means.
 2. A solid state switchaccording to claim 1 in which the bight of the electrically conductiveU-shaped clip is formed with a plurality of laterally extending smoothwave like depressions to increase the surface of contact engagement andenhance the bias of the clip against the electrical resistor means.
 3. Asolid state switch according to claim 1 in which the aperture in thecasing wall is located in the bottom wall, the means disposed on thebottom wall comprises an electrically conductive plate formed ofmaterial having good spring characteristics, the plate is formed with aplurality of laterally extending smooth wave like depressions toincrease the surface of contact engagement and enhance the bias of theplate against the electrical resistor means, and an arm depends from theplate and extends through the aperture in the casing bottom wall and iselectrically connected to electrical terminal means.
 4. A solid stateswitch according to claim 3 in which a second aperture is formed in acasing wall, the electrical resistor means comprises two disk-shapedelements each having two spaced faces, a face of one element inengagement with the electrically conductive plate, an electricallyconductive contact plate is interposed between the two elements, thecontact plate extends out of the casing through the second aperture andis connectable to an electrical source, and the electrically conductiveclip is in engagement with the other element.
 5. A solid state switchaccording to claim 1 in which the electrical resistor means comprises atleast one generally disk-shaped element composed of material having apositive temperature coefficient of resistivity.
 6. A solid state switchaccording to claim 5 in which the material is a doped barium titanate.7. A solid state switch according to claim 5 in which the electricalresistor means comprises two such generally disk-shaped elements.
 8. Asolid state switch according to claim 1 in which the means disposed onthe bottom wall comprises a flat plate which extends substantiallyacross the switch cavity.
 9. A solid state switch according to claim 1in which the second aperture is formed in a casing wall and anelectrically conductive plate extends substantially across the switchcavity spaced from the bottom wall, the conductive plate also extendingthrough the second aperture and electrically connected to electricalterminal means, the electrical resistor means comprising two electricalresistors, the conductive plate being interposed between and inelectrical connection with the two electrical resistors.
 10. A solidstate switch according to claim 1 in which the casing is formed with aportion mounting female connectors for terminal pins, one femaleconnector electrically connected to the electrically conductive clip,another female connector electrically connected to a portion of themeans disposed on the bottom wall which is disposed outside the switchcavity.
 11. A solid state switch according to claim 10 in which bayonetterminals project from the female connectors below the bottom wall ofthe casing, the casing is provided with a leg depending from the bottomwall extending beyond the bayonet terminals to facilitate pushing of theswitch onto terminal pins.
 12. A solid state switch according to claim11 including a plurality of stop surfaces projecting from the casingadjacent the female connectors to limit motion of the switch ontoterminal pins.
 13. A solid state switch according to claim 10 in whichthe legs of the U-shaped clip have laterally extending tabs at theirface distal ends, the said one female connector having a portionextending therefrom welded to one of the tabs of the clip.
 14. A solidstate switch according to claim 1 in which the casing is formed with aportion mounting female connectors for terminal pins, the legs of theU-shaped clip having laterally extending taBs at their free distal ends,one female connector having a portion extending therefrom welded to oneof the tabs of the clip, the other clip tab welded to a portion of themeans disposed on the bottom wall which is disposed outside the switchcavity, the electrical resistor means comprising two stacked resistorelements, electrical contact means interposed between the two resistorelements and electrically connected to another female connector.
 15. Asolid state switch comprising a casing having first and second portions,a plurality of apertures in the first portion, female pin connectorsreceived in the respective apertures, a second portion defining a switchcavity and having an open end, disk-like means having a positivetemperature coefficient of resistivity received in the cavity, anelectrically conductive clip received over the open end of the secondportion and biased against the disc-like means, and means electricallyconnecting the clip and a portion of the disc-like means spaced from theclip to respective female pin connectors.